Counterfeiting and piracy are major threats faced by nations across the world, both politically and economically. Several approaches have been suggested to solve this problem. For example, WO/2006/086008 discloses nanoparticles as covert taggants in currency, bank notes, and related documents; U.S. Pat. No. 6,692,030 discloses security document with nano-patterns; WO/2008/010822 discloses authenticating and identifying objects using nanoparticles; (WO/2008/030219) discloses remote identification of explosives and other harmful materials; U.S. Pat. No. 6,515,749 discloses sensitive and selective chemical sensor with nanostructured surfaces; (WO/2007/149120) discloses arrays of nano structures for surface-enhanced Raman scattering; U.S. Pat. No. 6,610,351 discloses Raman-active taggants and their recognition; U.S. Pat. No. 5,853,464 discloses pigment compositions; Spectroscopy, Feb. 26, 2004, discloses fluorescence detection of counterfeit US currency; and Microelectron. Eng., 2003, 65, 439, discloses microrelief structures for anti-counterfeiting applications.